The present invention relates to an infrared absorption filter. More particularly, the present invention relates to an infrared absorption filter which contains few foreign materials causing optical defects, has high transmittance in the visible light region, and manifests wide absorption in the near infrared radiation region and intercepts infrared radiation.
The following filters have been conventionally used as an infrared absorption filter such as a heat ray-absorbing filter or a filter for adjusting the visibility of a video camera:
(1) a filter composed of phosphate glass containing metallic ions such as copper or iron ions (Japanese Unexamined Patent Publication No. 235740/1985, Japanese Unexamined Patent Publication No. 153144/1987, etc.);
(2) an interference filter having plural layers differing from each other in refractive index on a substrate to allow light of specific wavelength to pass by interference of transmitted light (Japanese Unexamined Patent Publication No. 21091/1980, Japanese Unexamined Patent Publication No. 184745/1984, etc.);
(3) an acrylic resin filter composed of a copolymer containing copper ions (Japanese Unexamined Patent Publication No. 324213/1994); and
(4) a filter composed of a binder resin and a coloring matter dispersed in the binder resin (Japanese Unexamined Patent Publication No. 21458/1982, Japanese Unexamined Patent Publication No. 198413/1982, Japanese Unexamined Patent Publication No. 43605/1985, etc.).
Also, various materials have been conventionally investigated as a transparent magnetic wave absorption material, and examples thereof include the following materials. Further, a lot of materials combining them have been suggested.
(5) a magnetic wave shielding material composed of textile of conductive fiber;
(6) a magnetic wave shielding material having a mesh structure produced by etching a thin metal plate; and
(7) a magnetic wave shielding material composed of a thin film produced from high conductive metals such as silver and the like, and transparent conductive materials such as ITO, SnO2 and the like, using sputtering, vacuum deposition method and the like.
However, the above-mentioned conventional infrared absorption filters have problems as described below.
The filter (1) exhibits sharp absorption in the near-infrared region and can intercept infrared radiation at a very high ratio. However, the filter (1) pronouncedly absorbs part of red color in the visible light region so that the transmitted color looks blue. For display purpose, importance is laid on a color balance. In such purpose, it is unsuitable to use the filter (1). Another problem is raised about the processability of the filter (1) because it is made of glass.
The optical properties of the filter (2) can be freely designed. Further a a filter having properties almost equal to the designed properties can be produced. However, the filter (2) necessitates a plurality of layers differing in refractive index from each other for this purpose, consequently entailing a drawback of incurring high production costs. Moreover, when a large area is required, the filter (2) should have a uniform thickness of high precision over the entire area, resulting in a difficulty in producing the filter.
The filter (3) has improved processablity, a draw back of the filter (1). However, the filter (3) has low degree of freedom in designing optical properties as in the filter (1). Also there remains the problem of the filter (1) that it absorbs part of red color in the visible light region so that the transmitted color looks blue. Further, the absorption of copper ions is low and the amount of copper ions which can be contained an acrylic resin is restricted, causing a problem that the thickness of the acrylic resin has to be increased.
In the filter (4), various infrared-absorbing materials can be used. Examples of useful materials are phthalocyanine, nickel complex, diimmonium salts, azo compounds, polymethines, diphenylmethane, triphenylmethane, quinone and the like. However, when singly used, these materials pose problems of showing insufficient absorption or absorbing a visible light of specific wavelength in the visible light region. Therefore, a plurality of coloring matters are used together. However, when a filter containing a plurality of coloring matters in an infrared absorption layer is left to stand at a high temperature or a high humidity for a long time, the filter causes problems of denaturing a coloring matter due to decomposition and oxidation there of, bringing about absorption in the visible light region, or ceasing absorption in the infrared region, and the like. Further, when these filters comprises a substrate film coated with an infrared absorption layer, there occurs also a problem of deteriorating beam transmission property due to transmittance and haze value of the substrate film.
The above-mentioned problems are not improved even if the above-mentioned infrared absorption filters (1) to (4) are combined with the above-described magnetic wave absorption material (5) to (7).
PDP developed recently as a thin display having a large screen may invite error movement of a remote controller and the like due to near-infrared radiation discharged from the front surface thereof, consequently necessitating setting of an infrared absorption filter which cuts this near-infrared radiation, in front of the screen. However, this infrared radiation shielding filter also does not attain sufficient requirement in the above-mentioned infrared absorption filters, under current condition.
In the filter (4), when a diimmonium salt-based compound is used as an infrared absorption coloring matter, a filter can be obtained which surmounts the above-mentioned problems, provides high absorption in the near-infrared region, and manifests low absorption in the visible region. Further, it can provide an ability also suitable as an infrared absorption filter for PDP.
However, when an foreign material is present in a raw material resin of a substrate film of an infrared absorption filter, molecular orientation of the film is disturbed around this foreign material, in a stretching process in film formation. Resultantly, optical strain occurs, and the foreign material is recognized as a defect larger than the real size, causing remarkable deterioration in grade. For example, even an foreign material having a size of 20 xcexcm is usually recognized optically as a size of 50 xcexcm or more, and further, in some cases, it is recognized as an optical defect having a size of 100 xcexcm or more. For obtaining a film having high transparency, no inclusion of a particle which is used for imparting slipperiness in a substrate film, or an amount of inclusion of a particle as low as possible is preferable. However, when the content of a particle is smaller, transparency of a film tends to increase, and an optical defect due to a fine foreign material tends to more clear. Further, the thickness of a substrate film of this infrared absorption filer is usually 50 xcexcm or more, and the content of foreign material along the thickness direction per unit area of a film tends to larger in such a thick film as compared with a thin film, consequently, further raising this problem.
Moreover, when no particle is contained in a substrate film or the content of a particle is so lowered that transparency is not disturbed for imparting slipperiness in a substrate film, it is usually necessary that particles intending impartment of slipperiness are contained in an easy adhesion layer, and these particles have to be extremely small so as not to cause disturbance of transparency. However, fine particles having lower particle size tends to coagulate extremely, revealing possibility of formation of a coarse coagulated material. If an easy adhesion layer containing this coarse coagulated material is laminated on a substrate film, this coarse coagulated material becomes an optical defect.
A first object of the present invention is to provide an infrared absorption filter which has absorption in the near-infrared region, manifests high light transmittance in the visible region, does not have large absorption of a specific wavelength in the visible region, and has little optical defect.
Further, an object of the present invention is to provide an infrared absorption filter excellent in environmental stability and durability.
Further, a second object of the present invention is to provide the above-mentioned infrared absorption filter revealing blue gray tone.
The present invention has been completed in view of the above-mentioned conditions, and infrared absorption filters which can solve the above-mentioned problems are as follows.
A first aspect of the present invention is an infrared absorption filter comprising an infrared absorption layer laminated at least on one surface of a transparent polymer film, wherein said transparent polymer film is a film comprising a polymer easy adhesion layer laminated at least on one surface, said transparent polymer film contains substantially no particle, and said transparent polymer film contains foreign materials having a size of 20 xcexcm or more in an amount of 10/m2 or less per unit area of the film.
A second aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said infrared absorption filter has a transmittance of at most 30% in the near-infrared region in the wavelength range of 800 to 1100 nm, a difference of 10% or less between a maximum value and a minimum value of transmittance in the visible light region in the wavelength range of 450 to 650 nm, and a transmittance of not lower than 50% at a wavelength of 550 nm.
A third aspect of the present invention is an infrared absorption filter according to Invention 2, wherein said infrared absorption filter has a maximum transmittance of not higher than 30% in the near-infrared region in the wavelength range of 800 to 1100 nm, a difference of 10% or less between a maximum value and a minimum value of transmittance in the visible light region in the wavelength range of 450 to 650 nm, and a transmittance of not lower than 50% at a wavelength of 550 nm, even after being left to stand in the atmosphere at a temperature of 60xc2x0 C. and a humidity of 95% for 500 hours.
A fourth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said infrared absorption filter has a transmittance of not higher than 10% in the near-infrared region in the wavelength range of 900 to 1100 nm, a minimum transmittance of not lower than 60% in the visible light regions in the wavelength range of 440 to 500 nm and the wavelength range of 640 to 700 nm, a maximum transmittance of not higher than 60% in the visible light region in the wavelength range of 550 to 600 nm, and a transmittance of not lower than 50% at a wavelength of 550 nm.
A fifth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said infrared absorption layer comprises an infrared absorption coloring matter and a polymer resin as a main constituent component, and at least two or more selected from the group consisting of diimnonium salt-based compounds, phthalocyanine-based compounds and nickel complex-based compounds are contained as said infrared absorption coloring matter.
A sixth aspect of the present invention is an infrared absorption filter according to Invention 5, wherein at least a diimmonium salt-based compound is contained and at least any one selected from fluorine-containing phthalocyanine-based compounds and nickel complex-based compounds is contained, as said infrared absorption coloring matter.
A seventh aspect of the present invention is an infrared absorption filter according to Invention 5, wherein said diimmonium salt-based compound has a structure of the general formula (1): 
(wherein, R1 to R8 may be the same or different and represent a hydrogen atom, alkyl group, aryl group, alkenyl group, aralkyl group or alkynyl group. R9 to R12 may be the same or different and represent a hydrogen atom, halogen atom, amino group, amide group, cyano group, nitro group, carboxyl group or alkyl group. Any of R1 to R12 may have a substituent providing it can be bonded to a substituent. Xxe2x88x92 represents an anion.).
An eighth aspect of the present invention is an infrared absorption filter according to Invention 5, wherein said phthalocyanine-based compound is a fluorine-containing phthalocyanine-based compound.
A ninth aspect of the present invention is an infrared absorption filter according to any of Invention 5, wherein said nickel complex-based compound has a structure of the general formula (2): 
(wherein, R13 to R16 may be the same or different and represent a hydrogen atom, halogen atom, alkyl group, alkoxy group, aryl group, aralkyl group or amino group.).
A tenth aspect of the present invention is an infrared absorption filter according to any of Invention 5, wherein, regarding the amounts of infrared absorption coloring matters contained in said infrared absorption layer, the compounding ratio of a phthalocyanine-based compound is 0.01 to 1.2 parts by weight and the compounding ratio of a nickel complex-based compound is 0 to 1 part by weight based on 1 part by weight of a diimmonium salt-based compound.
An eleventh aspect of the present invention is an infrared absorption filter according to Invention 5, wherein the glass transition temperature of the polymer resin, a constituent component of said infrared absorption layer is from 85 to 150xc2x0 C.
A twelfth aspect of the present invention is an infrared absorption filter according to Invention 5, wherein said polymer resin contains a polyester resin as a main component.
A thirteenth aspect of the present invention is an infrared absorption filter according to Invention 12, wherein said polyester resin is a copolymerized polyester resin containing an alicyclic diol component of the general formula (3): 
(wherein, R17 and R18 represent a hydroxyl group and/or a hydroxyalkylene group having 1 to 8 carbon atoms and/or a group obtained by adding 1 to 10 alkylene oxides to a hydroxyalkylene group having 1 to 4 carbon atoms.) in an amount of 60 mol % or more as a polyhydric alcohol component.
A forteenth aspect of the present invention is an infrared absorption filter according to Inventions 1, wherein the amount of a remaining solvent in said infrared absorption layer is 0.05 to 5% by weight.
A fifteenth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said infrared absorption layer is laminated on the transparent polymer film according to a coating method.
A sixteenth aspect of the present invention is an infrared absorption filter according to Inventions 1, wherein said transparent polymer film is a biaxially stretched polyester film.
A seventeenth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said polymer easy adhesion layer contains a copolymerized polyester resin and a polyurethane-based resin.
An eighteenth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein the proportion of coarse materials having a maximum diameter of 100 xcexcm or more present on the surface of and/or in said polymer easy adhesion layer is 3/m2 or less.
A ninetieth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said polymer easy adhesion layer,contains a particle.
A twentieth aspect of the present invention is an infrared absorption filter according to Invention 1, wherein said transparent polymer film has a haze value of 1% or less.
A twenty first aspect of the present invention is an infrared absorption filter according to Invention 1, wherein a reflection prevention layer is laminated on the outermost layer of said infrared absorption filter.
A twenty second aspect of the present invention is an infrared absorption filter according to Invention 1, wherein an anti-glare treatment layer is laminated on the outermost layer of said infrared absorption filter.
A twenty third aspect of the present invention is an infrared absorption filter according to Invention 1, which is used as a member of a front plate of a plasma display.